A popular use for paint-ball guns is in recreation, where the participants fire paint-ball projectiles toward a target. The target may be a moving or stationary paper target used for target practice. The target might be another participant in a game, where the participants are attempting to strike each other with soft paint-filled projectiles. Paint-ball guns fire a plastic-walled, paint- or gelatin-filled projectile using compressed gas as the source of power to accelerate the paint ball down a chamber and into a gun barrel. The paint ball enters the barrel from a hopper at the breech end, is accelerated by compressed gas, and exits the muzzle of the barrel.
Prior art in the area of air-powered guns, and especially paint-ball guns, uses canisters of liquid CO2 or other compressed gas communicated through regulators to provide a regulated gas pressure to the gun. Whether the paint ball is spinning, and in what direction, when it exits the barrel, affects its trajectory. The conventional paint ball barrel pushes the ball down the barrel with no controlled spin and many times with no or very little ball rotation. Much like a pitcher's knuckleball, the paint ball will move erratically as the ball exits the barrel, due to the supercritical eddy currents behind the ball. The paint ball moving with no rotation develops pressure forces in front of the ball, and eddy currents with supercritical air flow immediately behind the ball resulting in the ball moving erratically. Further, the ball with no rotation develops significantly more drag in front of the ball as it moves through the air.
Paint balls have a liquid center covered by a thin plastic or gelatin membrane that maintains the paint ball in an approximately sperical shape. This soft formation and thin-walled construction cause frequent deformities in the shape of the paint ball, making it less than perfectly round. A seam is formed in the plastic membrane during manufacturing, which also tends to interrupt the otherwise smooth exterior surface of the plastic membrane. Because paint balls come in various diameters, the air pressure used to accelerate the ball is affected by any diameter difference between the ball and the barrel.
The lack of consistency in size and shape of the paint ball ammunition can further be affected by temperature and humidity of the site of use. Humid weather tends to swell the paint balls because the water in the air softens the plastic membrane defining the dimensions of the ball. Hot weather increases the volume of the paint contained in the ball, and thus also affects the overall dimensions of the paint ball by pressing outward on the plastic membrane cover.
Since paint balls may thus have different diameters due to manufacturing tolerances and expansion because of heat or humidity, paint-ball guns typically use a “ball sizer” attachment between the breech of the gun and the barrel. The paint ball enters the ball sizer first and is accelerated there by gas pressure to essentially its maximum velocity before entering the barrel of the gun. The user chooses a ball sizer of the appropriate diameter to match as nearly as possible the size of the paint balls he is using at that time. Ball sizers typically connect with a barrel and with the breech of the gun with threaded joints.
The seam in the paintball has a natural tendency to spin the paint ball as the ball passes through the ball sizer, resulting in erratic spinning of the ball and an erratic trajectory. If the entrance to the ball sizer, or the joint between the ball sizer and the barrel, catches the seam of the ball, the ball will also have an erratic spin. In some cases, this catching of the seam will cause the ball to rupture before leaving the barrel.
Conventional smooth-bore paint ball gun barrels do little to rectify the ball spin caused by the imperfect paint-ball exterior surface and the variance in size caused by manufacturing or temperature and humidity. Paint balls expanded from humidity or temperature spin worse on exit from the gun barrel due to increased contact with the sidewall of the barrel bore if the contact with the barrel is not a controlled contact. Imperfect surfaces, such as the seam of the paint ball, also impart spin to the exiting paint ball due to contact with the interior surface of the gun barrel. Combinations of temperature, size differential, and surface imperfections can combine to affect the trajectory of an exiting paint ball severely, and render the accuracy of the gun to a very poor state. Therefore, it is important to smoothly accelerate the ball to its maximum velocity in the ball sizer.